The ultimate authority for marriage law in the US is the individual States, the Federal government has no jurisdiction so the poster you are responding to was comparing apples to apples for all practical purposes.

An inordinate number of laws in the US are de facto “national” only because all States recognize similar laws, not because there is actually a national law. The Federal government doesn’t have the authority to enact most laws. It is the same reason the US does not have a national ID, why corporations are solely creatures of individual States, and why public health policy is decided by States (see: COVID).